1. Field of the Invention
This invention relates to a time code signal recording circuit suitably applied to a video tape recorder of the type which records a time code signal together with a video signal.
2. Description of the Prior Art
A video tape recorder for a broadcasting station or a video tape recorder for recording and reproducing a video signal of a high definition television system normally records, in addition to a video signal and a control signal, a time code signal for controlling such video signal for each frame or for each field.
A tape feeding system of an exemplary one of such conventional video tape recorders is shown in FIG. 3. Referring to FIG. 3, the tape feeding system shown includes a rotary drum 3 for feeding a magnetic tape 2 accommodated in a video cassette 1. Where the video tape recorder is designed for a high definition television system, since it is necessary to record or reproduce a video signal in a plurality of channels, a pair of magnetic heads (not shown) disposed adjacent each other and another pair of similar magnetic heads (not shown), and accordingly a total of four magnetic heads, are disposed in an angularly spaced relationship by about 180 degrees from each other on the rotary drum 3. The wrapping angle of the magnetic tape 2 on the rotary drum 3 is substantially equal to 180 degrees.
A composite head 4 is disposed adjacent a route of the magnetic tape 2 outside the video cassette 1 and includes a control head (not shown) disposed on an upper stage side for recording and reproducing a control signal CTL and a recording head disposed on a lower stage side and integrated with the control head for recording and reproducing a time code signal TC, that is, a time code head (not shown). The control head and the time code head, however, may otherwise be formed as separate members from each other.
Referring now to FIG. 4, there is shown an exemplary tape format when such video tape recorder as described above is used. A video signal is helically recorded simultaneously for two channels onto a pair of video tracks 10 of a magnetic tape 2 by such magnetic head arrangement as described above. A pair of digital audio tracks 11 are formed on extension lines of the video tracks 10. An analog signal is recorded onto an audio track 12 separately from a digital audio signal. The audio track 12 is formed along a longitudinal direction of the magnetic tape 2. A control signal CTL and a time code signal RECTC are recorded onto a control track 13 and a time code track 14, respectively, by the composite head 4 described above.
A time code signal RECTC to be recorded onto the time code track 14 is produced by such a recording circuit 19 as shown in FIG. 5. Referring to FIG. 5, the recording circuit 19 includes a reference frame signal generating circuit 21 for generating a reference frame signal REF which is such a rectangular wave signal of 60 Hz as seen from a waveform A shown in FIGS. 6(a) to 6(b). The reference frame signal REF thus generated is supplied to a time code signal generating circuit 22, at which such a time code signal RECTC which is synchronized with the reference frame signal REF as seen from another waveform B of FIG. 6 is generated. The time code signal RECTC thus generated is recorded by means of the composite head 4 (more particularly, the time code head of the composite head 4).
By the way, relative positions of a video signal, a control signal and a time code signal on such magnetic tape 2 are determined in advance depending upon a tape format. Since the relationship between a video signal and a time code signal depends upon a relationship between a tape pass system of the magnetic tabe 2 wrapped on the rotary drum 3 and the location or mounted position of the composite head 4, when the accuracy in mounting of the composite head 4 is low and the composite head 4 is not mounted at a prescribed position, the position of a time code signal RECTC recorded on the magnetic tape 2 will be different from the specific position of the tape format.
In such instance, it is a conventional countermeasure either to finely adjust the location of the composite head 4 or to mechanically work the associated elements with a high degree of accuracy. However, even where the mechanical accuracy is sufficiently high, it is still impossible to eliminate such adjustment. Thus, it actually is a conventional practice to perform fine adjustment of such composite magnetic head 4 for each of products when it is shipped from a factory.